Polarforschung 68: 267 - 274,1998 (erschienen 2000)
Teetonics and Sedimentation of the Meso- to Neoproterozoic Timan-Varanger Belt along the Northeastern Margin of Baltica
By Vsevolod G. Olovyanishnikov', David Roberts? and Anna Siedleekat
THEME 8: Polar Urals, Novaya Zemlya and Taimyr: The North "Tirnanides'. Subsequent research by several Russian scientists, ern Connection of the Uralides in particular ZHURAVLEV and co-workers (e.g. ZHURAVLEV & GAFAROV 1959, ZHURA VLEV & OSADCHUK 1960, 1962, Summary: Extending from the Timans in the southeast to the Varanger Penin ZHURAVLEV 1972) and RAZNITSYN (e.g., 1962, 1968), brought a sula in the northwest, the Timan-Varanger Belt (TVB) comprises predominantly wealth of data and ideas on several aspects of the geology of the terrigenous Neoproterozoic successions, defonned and metamorphosed at corn paratively low grade during the Timanian (Baikalian) orogeny, an event broadly Timans and also on the relationship between this Neoproterozoic equivalent to the Cadomian 01' western Europe, In Neoproterozoic time the TVB fold belt and the pre-Palaeozoic substratum of the Pechora Ba formed the faul ted, extensional southwestern margin 01' an oceanic basin, the sin, In addition, several decades of research by GETSEN (sum central parts 01' which are buried beneath the Palaeozoic and youngcr cover 01' marised in OLOVYANISHNIKOV 1975, 1987, 1998) have resulted the Pechora Basin. The major structural element 01' the basin margin is a NW SE-trending fault zone thar separated two domains 01' sedimentation; pericratonic in further and considerable progress in our knowledge of the to the southwest and basinal to the northeast, which show contrasts in both thick geology of the Timanides, ness and sedimentary fucies. In the Timan-Kanin-Pechora part 01' the basin, sedi mentation began already in the Middle Riphean, and by Late Riphean time a The northwestern extension ofthe Timanian mountain chain was prominent stromatolitie carbonate ramp formation had built up along the shelf margin. In the NW Kola- Varanger region, however, sedimentation did not start postulated by RAMSAY (1899) and TSCHERNYSCHEV (1901) to oc until thc (?)Middle-Late Riphean. Thus, with time, the basin extended cur along the northeastern Murmansk Coast of the Kola Penin northwestwards anelsedimentation, including deposition ofVarangerian tillites sula, on Rybachi, Sredni and Kildin, and to continue far into in the northwest, continued into the Vendian period. The fault zone which formed northern Norway. Potential field and seismic ret1ection data in the extensional margin of the basin was reactivated during the Timanian orogeny and again in later periods. The Timanian deformation in these exposed marginal offshore areas has confirmed the presence of these folded rocks areas involved basinal inversion, folding and oleavage development, arising from immediately northeast of Kola (e.g., BOGATSKY et al. 1996), SW-directed compressivc stresses, the main phasc 01' these movements dating Recently, a modified version of this idea, which had been ac to about 600-575 Ma, A variety 01' felsic to mafic plutons and dykes intruded cepted for decades in several large-scale geological interpreta the folded rocks 01' thc TVB. tions, received new support from some of the results of a joint Both seismic reflection and deep drill hole data have shown that Meso- to Neo Norwegian-Russian research programme carried out during the proterozoic strata in the prc-Palaeozoic basement of thc Pechora Basin are more years 1989-95 on the coastal Neoproterozoic occurrences ofthe intcnsivcly deformed and metamorphoscd and also include oceanic and are Kola Peninsula and on Varanger Peninsula in Norway (see in volcanic scqucnccs and diverse plutonic rocks. Fragments 01' older basement terranes arc also present. Timanian deformation beneath the Pechora Basin was ROBERTS & NORDGULEN 1995). The latter area, now inferred to thus much more intcnsc and involved the telcscoping 01' arcs, are roots and expose the northwesternmost segment of the proposed chain, microcontinental terranes in a more complex accretionary zone, generally re had already been thoroughly mapped and studied by geologists fcrrcd to as the Pechorskaya eollision zone. of the Geological Survey of Norway and other western work ers since the mid-1960s. Finally, all three authors ofthis paper together visited the Central Timans in 1995 (OLOVY ANISHNIKOV INTRODUCTION et al. 1997).
The Timanian mountain chain, an important regional element The objective of this contribution is to outline the recent pro in Circum-Barentsian geological structure, was first recognised gress and understanding of this about 1800 km-long Neopro almost precisely 100 years ago (RAMSA Y 1899, TSCHERNYSCI-IEV terozoic structural element occurring along the northeastern 1901). SCHATSKY (1935, 1958) further developed this early idea perimeter of the Baltic Shield and Russian Platform. In the text and suggested that the chain represented part of a Late which follows we refer to Schatsky's "Timanides: as the Timan Precambrian Baikalian fold belt which he called the Varanger Belt (TVB) in which the Timans themselves consti tute the geographically most extensive, southeastern part.
1 Institute of Gcology, Komi Research Centre, Ural Division, Russian Academy of Sei Note: Neoproterozoic = Late (Upper) Proterozoic = 1000 (900) enees, Pervomaiskaya 54, Syktyvkar, 167000 Russia. Ma - 545 Ma = Late (Upper) Riphean and Vendian. Norges Gcologiske Undersokelse, N-7491 Trendheim. Norway Mesoproterozoic = 1600-1000 Ma = Lower (Early) and Mid Manusript received 14 Deeember 1998, accepled 12 Ocrober 1999. dIe Riphean.
267 STRATIGRAPHY AND SEDIMENTATION
Sediments and sedimentation realms: general features
The Meso- to Neoproterozoic strata of the Timan-Varanger Belt accumulated in response to extensiona1 faulting along the north eastern perimeter of the Fennoscandian Shield. The pre dominantly terrigenous sedimentary successions also include an extensive be1t of carbonate rocks in the Timan-Kanin zone. The rocks are for the most part metamorphosed at on1y very low grade. On the Kanin Peninsula and in northern Timans, how ever, metamorphic grade reaches up to amphibolite facies, par ticularly in the cores of anticlines. Two parallel, NW-SE trending, elongate, sedimentation domains are present adjacent to the major zone of faulting which played a crucia1 role in the development and character of sedimentation on either side of this structural element (Fig. 1). The fault zone exposed on the Varanger and Rybachi-Sredni Peninsulas, the Trollfjorden Komage1va Fault Zone (TKFZ) and Sredni-Rybachi Fault Zone (SRFZ), respectively, can be followed to the southeast along and just off the coast of the Kola Peninsula, partly with the help of geophysical data. It then extends across the Kanin Peninsula and into the Timans where it is known as the Central Timan Fault (CTF). It is fairly weIl documented that the CTF formed the southwestern margin of a Neoproterozoic (Riphean) basin bur ied beneath unconformably overlying Cambro-Ordovician rocks of the adjacent Pechora Basin where there are also several other parallel faults. The prolongations of these other faults beneath the Barents Sea are generally poorly known. The CTF-SRFZ Z TKFZ, on the other hand, not only continues throughout the A form of zonation in the Timans, involving lithology, con 9 trasting thicknesses and degree of metamorphism, but not sedi Fig. 1. Top: Outline map showing the Timan-Varanger Belt. KP - Kanin Penin mentation domains, had, in fact, already been suggested some sula; NT - Northern Timan; RP - Rybachi Peninsula; SP - Sredni Peninsula; VP 40 years ago (ZHURAVLEV & OSADCHUK 1960). - Varanger Peninsula; CTF - Central Timan Fault; ETF - East Timan Fault; WTF - West Timan Fault. The CTF is shown to continue to the Rybachi-Sredni and The lithological development of both the pericratonic and the Varanger Peninsulas where it is called Sredni-Rybachi Fault Zone and Trollfjorden-Komagelva Fault Zone, respectively. Shaded areas show the out basinal successions ofVaranger, Rybachi, Sredni, Kildin, Kanin, crop of the Neoproterozoic rocks. and northern and centra1 Timans varies considerably along Bottom: Simplified geological-structural map ofthe Timan Range and basement strike, a feature which is not unexpected in view of the great of the Pechora Basin. 1: Basement; 2: Pericratonic zone; 3: Carbonate shelf distances involved, the likely differential stresses operative margin; 4: Slope-to-basin zone; 5: Pechora collision zone 6: Outcrop of the Meso- to Neoproterozoic rocks; 7: Zone ofTimanian accretion, 8: Urals; 9: Line along the basin-margin faults, and a varying topography in the of the section, shown in Figure 4. WTF: West Timan Fault (also called the Pre adjacent source areas. These variables, along with the fact that Timan Fault); CTF: Central Timan Fault; ETF: East Timan Fault; NT: North the ages of the successions are generally only roughly deter ern Timan; PK: Pechora-Kozhva Fault; Kol. M.: L. Precambrian Kolguev mas mined by microfossils and indirectly by isotopic ages of sif or terrane; Kho.M.: L. Precambrian Khoreyver massif 01' terrane. Modified from OLOVYANISHNIKOV et al. (1997). transecting pre-Pa1aeozoic intrusions, make detailed correlation particularly speculative. Although lithostratigraphic correlations have been proposed by many geologists, it seems obvious that northeast. On Kildin Island, Varanger Peninsula and farther to lithologically similar units may weIl be diachronous, particularly the west, within the Caledonides, equivalent Upper Riphean as such great distances are involved along the belt. In the carbonate units are also pressent. Timans, a discontinuous belt of carbonate and carbonate terrigenous lithologies occurs between the pericratonic The time span during which the discussed sedimentary rocks ac terrigenous successions to the southwest and the basinal to the cumulated embraces more than 500 million years. Reso1ving the 268 history of the TVB in more detail would require stratigraphic unconformably overlain by the Early Vendian glacial depos techniques which are either not available (direct isotopic dating) its. or very general (biostratigraphy), a fact which poses fundamen tal problems in work on Precambrian (meta)sedimentary rocks in general. Isotopic ages There is a considerable number of published isotopic ages on the Biostratigraphie evidence intrusive and hypabyssal rocks of the central and northern Timans and the Kanin Peninsula, as weil as some ages on dolerite dykes Microfossils and columnar stromatolites provide the biostra that transect the Upper Proterozoic deposits along the tigraphic evidence of the age of these diverse Neoproterozoic northwesternmost periphery of the Timan-Varanger Belt. AKIMOVA successions. In arecent paper, OLOVYANISHNIKOV (1998, pp. 103 (1980) published a synopsis of 141 K-Ar (whole-rock) ages of 108) presented an extensive review of all microfossils found in magmatic rocks and 32 ages of metasedimentary rocks (whole the Neoproterozoic strata of the Timans and Kanin. Taxa of rock and minerals) produced by several Russian authors since the acritarchs referred to in this synopsis were identified by several mid-1960s. Although the reliability of much of these data is in scientists but only a few had been reported earlier (e.g. GETSEN doubt, the majority ofthe ages indicate Late Riphean to Vendian & PIHOVA 1977). While the assemblages are suggestive mostly minimum ages and thus they do not contribute to any refinement of a Late Riphean to Terminal Riphean (Kudash) age, some of the Neoproterozoic stratigraphy. They do, however, provide forms, according to the author, do not preclude a partly Vendian some information concerning the timing of metamorphic and de age for the youngest sedimentary rocks both in central and in formation events. Recent work by ANDREICHEV (1998) on Rb-Sr northern Timans. However, in the revised list of microfossils (38 isotopic ages of intrusions from northern Timan shows that the ma forms), two ofthese forms are Cambrian contaminations and the jority of dates fall between 500 and 800 Ma, confirming the remainder comprise partly Riphean acritarchs and partly forms Neoproterozoic minimum age of the dissected strata. Of interest, of long stratigraphic range not suitable for stratigraphie work however, is the 1100±39 Ma isochron age of a diabase transecting (Doc. M. Moczydlowska-Vidal, written communication 1998). the Proterozoic strata, indicating the possibility that also Middle Therefore, the postulated Vendian age of some of the strata in Riphean metasedimentary rocks may occur in this area. In this con central Timan is uncertain. nection it is worth mentioning that AKIMOVA(1980) also reported 23 whole-rock and mineral age detenninations of c. 1000-1500 Ma Microfossils extracted from the Neoproterozoic sections of the (even >2000 Ma in three cases), mainly of metadiabases and coastal areas of Kola Peninsula (the Murmansk Coast in the diabases cutting the carbonate rocks of central Timan (AKIMOVA northeast and the Tiersky Coast on the White Sea) were stud 1980, Table 2, nos. 40-62 and p. 83). Another group of dates für ied in detail by Mikhailova (LYUBTSOV et al. 1989). She de diabases transecting the carbonate rocks (from borehole cores) lies scribed a collection of 151 specimens comprising 43 forms of in the range 600-700 Ma, which is in accord with the Late Riphean acritarchs, ten of which were determined at generic level. Only age of the carbonate succession indicated by columnar eight of these forms are known to cross the Riphean-Vendian stromatolites (see above). Assuming that the sampling and dating boundary; however, they are not diagnostic of the Vendian. procedures are reliable, these various data would suggest the pres Michailova (LYUBTSOV et al. 1989) concluded that the upper ence oftwo separate carbonate successions, one of Early 01' Mid formations of the basinal zone of Rybachi may possibly be dIe and the other of Late Riphean age. Recently, OLOVYANISHNIKOV Riphean-Vendian due to the fact that the assemblage there is (1998: 116-117), in his summary interpretation of the Meso- to very impoverished compared to the rich Riphean assemblages Neoproterozoic stratigraphy ofthe Timans and Kanin Peninsula, found elsewhere. This fact, however, in our view, is only what has suggested that the carbonate rocks both in central Timan and can be expected in a rapidly deposited, mostly coarse-grained farther north are stratigraphically subjacent to the remainder ofthe succession accumulated predominantly on a submarine fan Upper Precambrian successions. This suggestion is based on the (SIEDLECKA et al. 1995). SAMUELSSON (1995, 1997) examined a high er metamorphic grade of the carbonate unit in central Timan new collection of arcritarchs from Sredni and concluded that compared to that of adjacent terrigenous units. Although this does these pericratonic strata are of Late to Latest (Karatavian) not seem to constitute sufficient evidence it is, however, in accord Riphean age. In fact, only on the Varanger Peninsula have ance with the group of high radiometric ages reported by AKIMOVA Vendian strata been positively identified in the pericratonic (1980). There would thus appear to be a serious new implication, zone; and, in addition, in that particular area there also occur the namely, that there are two carbonate successions in the Timans of weil known Varangerian tillites of earliest Vendian age. These considerably different age. are absent in the remainder of the Timan-Varanger Belt. This review of the data shows that the isotopic ages, which are Columnar stromatolites, occurring in the carbonate formations relevant to the timing of deformation that will be discussed later of the Timans, the Kanin Peninsula, the coastal areas of the Kola in this contribution, do not provide any important evidence use Peninsula and the pericratonic carbonates of northern Norway, ful for refining the chronostratigraphy. The >1000 Ma ages of all indicate a Late Riphean age for these carbonate accumula mafic intrusive rocks, however, do confirm that sedimentation tions (BERTRAND-SARFATI & SIEDLECKA 1980, RAABEN 1975, in the Tirnan-Varanger Basin commenced in Late 1994: 48, RAABEN et al. 1995). On Varanger Peninsula they are Mesoproterozoic time. 269 TECTONICS AND SEDIMENTATION: A TENTATIVE 3. The geophysical data which help to link the separate areas MODEL of outcrop; 4. The weIl exposed and documented Neoproterozoic geology Although we are fully aware that the stratigraphie record in parts of the Murmansk Coast and the Varanger Peninsula, which of the belt is fragmentary and uncertain, we nevertheless believe serve in many respects as a 'key' to our understanding of the that the data that are available are sufficient to warrant the pres remainder of this extensive belt. entation of a model integrating tectonics and sedimentation in the Timan-Varanger Belt, taking into account the following cri In response to the initial rifting and downfaulting (Fig, 2A), teria: sedimentation probably began already in the Middle Riphean 1. The possible existence of strata older than Upper Riphean (?or earlier) in the Timans and Kanin Peninsula while in the in the central and northern Timans and on Kanin (see above northwest, along northeastern Kola and on Varanger, it did not and also e.g. GETSEN 1987, his Fig. 2); start until the Late Riphean. This suggests that the basin was 2. The thicknesses and sedimentary facies of the pericratonic extending northwestwards with time. While the TVB represents and basinal successions; the southwestern marginal area of the opening and deepening basin, its more central areas now form the basement to the Pechora Basin, which is a complex mosaic of oceanic crust, is A land are material and microcontinental fragments cut by Riphean and Vendian (Timanian) plutons (BELYAKOVA & STEPANENKO 1991, GETSEN 1991, BOGATSKY et al. 1996, GEE et al. 2000). This scenario is largely in agreement with a previous1y postulated 'Timan-Ural Geosyncline Model', i.e., an extensive eugeoclinal -\- + basin of which the Timan-Kanin zone constituted only the south CTF-\' + western marginal part, closest to the craton beneath the Russian P1atform (e.g. ZHURAVLEV & GAFAROV 1959, ZHURAVLEV 1972, GETSEN 1987). Consequently, an alternative, previously sug gested fixist 'Aulacogen Model', invo1ving a major graben, separated from the Polar Urals by a cratonic block (BOGDANOV 1961, SCHATSKY 1964, SIEDLECKA 1975, IVANOV 1981), has now been abandoned. Within the TVB, i.e. the marginal part of the basin, truncation c of the rift shou1ders and erosion on the footwall side occurred + in response to the fault-generated relief, and the bypassing + + sediments were eventually accumu1ated in the slope-to-basin + + + area (Fig. 2B). Basinal accumulations in the Timans and on Kanin are fine-grained, partly fine turbidites, a fact which indi cates that the slope was gentle, and that subsidence and sedi mentation were close to equilibrium (SIEDLECKA & ROBERTS 0 1995). In the northwestern extremity of the basin, on the other - .. hand, there are both olistostromes and coarse turbidites in the basinal zone, reflecting the existence of a steep slope with fast + + + + + + + subsidence and rapid to locally violent sedimentation (SIEDLECKA et al. 1995). As the relief gradually decreased the basinal sedi mentation became slower and the basin filled out, while the E pericratonic sedimentation started lapping off, with sediments eventually accumulating upon the proximal part of the basinal + + + infill (Fig. 2C). + + v-er + + + The final phase of sedimentation in the proposed model was + + characterised by slow sedimentation in the pericratonic areas only, mainly reworking and gradually increasing the maturity of the shaIlow-marine clastics with little new sediment deliv ery. This situation created favourable conditions for the devel Fig. 2: Tentative model for the dcvelopment of the Timan-Varanger Basin. A: opment of stromatolites and carbonate precipitation in the ma initial rifting; B: Erosion of the footwall shoulders and aeeumulation of slope rine waters no longer heavily charged by suspended terrigenous to-basin deposits; C: shallow-marine pericratonic terrigenous sedimentation and fines. A rimmed terrigenous-carbonate ramp was thus created stromatolitie reefs; D: accumulation of shelf-margin ramp carbonates; E: De formation due to SW-direeted compressive stress (open arrow) and inversion of (Fig. 2D). The proposed succession of events provides an evo basin-marginal faults. CTF - Central Timan Fault; WTF - West Timan Fault. lutionary framework to be tested, refined and modified by fur- 270 ther studies; it is thus a tentative model, and is not in any way believed to have controlled the intrusion and ultimate distribu definitive. Contacts between the facies zones (pericratonic, car tion of gabbroic, picritic and syenitic magmas. Kimberlitic bonate, basinal) in the Timans and on Kanin are everywhere rocks, eruptive breccias and nepheline syenites have been re faulted and it is only in the northwestern peripheral parts of the ported from the areas of intersection of some of these NW-SE basin that the pericratonic Upper Riphean sedimentary rocks and NE-SW faults. actually rest upon the basinal deposits (erosional contact) and where the stromatolitic dolomites occur in the uppermost part of the fairly mature, pericratonic, terrigenous sedirnentary suc ASPECTS OF DEFORMATION AND METAMORPHISM cession. We have, in this model, purposely excluded the possi ble existence of an older carbonate unit (see above) since more Deformation of the discussed Riphean strata along the TVB is documentation is required in support of this hypothesis. In ad illustrated by the three summary sections in Fig. 3. All three dition, there are unconformities, within the pericratonic sections show that the structure is fairly simple, resulting from successions in particular, showing that there were varying rates TimanianlBaikalian basin inversion with the principal compres of sedimentation and subsidence. As a consequence, the detailed sive stress directed from northeast to southwest (present-day di infill history of the basin was much more complex than that rection). The intensity of deformation and metamorphism has outlined here. varied, however, in different parts of the belt. In the central Timans, SW-facing mesoscopic and larger-scale folds carry a A discussion of the abundant geophysical data that are available steep, NE-dipping, penetrative axial-planar cleavage of from the Timan-Kanin-Pechora region is outside the scope of anchizone grade. In northern Timan and Kanin there is a com this paper. Prominent positive, linear, magnetic anomalies of parable NW -SE fold axial trend but metamorphic grade is NW-SE trend parallel the regional strike in what is essentially higher, locally extending into amphibolite facies (GETSEN 1987: a 'magnetic minimum' domain. This anomaly trend is offset 67, compilation map). On Rybachi, the turbiditic succession is here and there by concealed NE-SW-trending faults which are pervasively cleaved and folded along a consistent NW-SE trend; A VARANGER PENINSULA \ / /'- ...... SW /- ... \,\ / - NE .-.::;;;:::...... "'~'/ ~ ...... ~' . ~~ • • r. , . .. . '. . . '.-:' . ..' .. . . z; ~.~~ . . + +' • • :.~ ,-' : '.' • . . . . . " ..-;-/... + + + + + + + +-"1' ? Based on Siedlecki 1980 B KANIN PENINSULA \ Palaeozoic \ \ Palaeozoic NE sw \ Based on Getsen 1987 c CENTRAL TIMAN SW ...... ',' ? Based on Getsen 1987 r:::l ....···· ~ ~ Basement 0. . . Pericratonic l2.J.2J Siope and basin Carbonate sedimentary sedimentary rocks rocks rocks Fig. 3: Summary cross scctions showing the main features of the structure in thc Timan- Varanger Belt (not to scale). 271 and the rocks are mostly in anchizone grade (RICE & ROBERTS ±39 Ma, an olivine-kersantite gabbro at 702 ±45 Ma and 1995). On Sredni and Kildin, diagenesis grade prevails. In east syenites and granites at c. 600 Ma. Finally, GEE et al. (2000) ern Varanger Peninsula, the NW-SE fold and cleavage trend is report single-zircon Pb-evaporation ages in the range c. 550-570 again recognised northeast of the TKFZ, dying out to the west Ma from post-tectonic granites and diorites taken from deep (ROBERTS 1995, 1996) where c. NE-SW-trending Caledonian drillcores in the Timanian 'collision zone' beneath the Pechora structures take over. Basin. These Late Vendian ages confirm the model of a Timanian basement to the Pechora Basin. The section across the western parts of the Varanger Peninsula (Fig. 3A) shows that the basinal succession which crops out Evidence from isotopic dating from the Rybachi-Sredni mainly northeast of the TKFZ is also present to the southwest, Varanger region bearing on the age of the basina1 inversion and a feature which is easy to explain by on1ap during infilling of associated penetrative cleavage is comparatively meagre at the basin. In addition, it has been shown that the pericratonic present, although work is in progress on dating the pervasive strata there overlie the basinal Riphean sediments over part of cleavage on Rybachi. A 4°Ar_39Ar laser microprobe study on the area, as documented by RICE (1994), while the bulk of the dolerite dykes transecting the folds and cleavage on Rybachi pericratonic succession, towards the southwest, rests directly on gave no definitive intrusive age, but suggested that they were the Lower Precambrian crystalline basement. The carbonate older than Ordovician model ages (ROBERTS & ONSTOTT 1995). deposits which terminate the pericratonic succession are not Palaeomagnetic data from these same dykes favoured a Late shown in this particular section. On the Kanin Peninsula, basina1 Vendian to Cambrian age (TORSVIK et al. 1995). One solitary deposits are separated from the Late Riphean stromatolitic dyke from Sredni gave a similar palaeomagnetic age, while the dolomites occurring in the southwest by a vast area underlain 4°Ar_39Ar analysis on this same dyke gave a minimum age of 546 by Palaeozoic strata which probably rest directly on basinal ±4 Ma. This dyke cuts a diagenesis-grade compactional fabric accumulations (Fig. 3B). There are, however, no exposures to that has been Rb-Sr-dated to 610-620 Ma (GOROKHOV et al. verify this interpretation, which is based solelyon geophysical 1995). Illite fractions from along the SRFZ on Sredni have data. Finally, the representative section from central Timan yielded a Rb-Sr maximum age of 570 Ma (GOROKHOV et al. shows that the basinal succession, the carbonate formation and 1995), which has been interpreted (ROBERTS 1996) as providing the pericratonic strata are in contact along major faults (Fig. 3C). an approximate age for the basinal inversion in this part of the Timan-Varanger Belt. Although we present a comparatively simple model for the ori gin of the rifted, extensional, southwestern passive margin of Isotopic age determinations from Varanger Peninsula are few the Riphean basin and its subsequent syn-metarnorphic, cleav in number. K-Ar whole-rock data on dolerite dykes cutting the age-related deformation (see also Fig. 2E), isotopic ages indi Late Riphean to Early Vendian strata showed three age group cate that deformation is likely to have occurred in more than one ings: (a) c. 360 Ma, (b) c. 650 Ma and (c) 945-1945 Ma Late Riphean-Vendian episode. The principal tectonothermal (BECKINSALE et al. 1975; recalcu1ated ages). One of the group (a) event, however, coeval with basinal inversion, is ascribed to dykes has provided a U-Pb zircon upper-intercept age of c. 567 what SCHATSKY (1958) defined as Baikalian orogenic move Ma (ROBERTS & WALKER 1997). This particular dyke cuts a ments, which he considered to be equivalent to the Cadomian cleavage which is interpreted as probably of Timanian age. episode of crustal deformation in other parts of Europe. While the Late Devonian K-Ar ages ofthis and possib1y other dykes on Varanger may relate in some way to a Late Devonian GETSEN (1987: 60), on the basis of K-Ar mineral ages thermal overprint event (see also LARSEN & TULLBORG 1998), this (amphibole, biotite, muscovite and K-feldspar), suggested that does not reject the possibility that some dykes may have intruded there were three episodes of metamorphism and magmatic ac in Devonian time. tivity in the northern Timan and Kanin Peninsula: at 680 ±20 Ma, 600 ±5 Ma and 530 ±5 Ma. For Central Timan, this same In summary, there is a good evidence in the Timans and Kanin, author (GETSEN 1987: 55) reported three groups of ages and now with support from isotopic studies on granites from (isochrons derived from sericite, phlogopite and K-fe1dspar): at deep drillcores beneath the Pechora Basin, that the peak 970 ±20 Ma, 725 ±25 Ma and 590 ±20 Ma. AKIMOV A(1980: 83 tectonothermal phase of the Timanian orogeny in this part of the 84) also considered that there were several magmatic and meta TVB occurred during approximately Mid Vendian time, c. 600 morphic events but believed that the main episode of rnetamor 575 Ma. Farther to the northwest, on Rybachi, Sredni and east phism and deformation occurred within the interval 570-680 ern Varanger, the temporal constraints at present are somewhat Ma. Another estimate, based on recalculated ages, was provided less precise. The character and trend of the foreland-facing fold by MALKOV (1992) who considered that the main tectono ing and cleavage in these areas, however, are remarkab1y simi metamorphic phase of the Timanides falls in the time range 600 lar to those encountered in the Timans. 575 Ma; and a second metamorphie stage is put at c. 505-470 Ma. The ages of c. 1000-1500 Ma, earJier reported by SIEDLECKA (1975: 329) and by AKIMOVA (1980), are also of interest in the THE TIMANS AND BASEMENT OF THE PECHORA BASIN light of the recent Rb-Sr work by ANDREICHEV (1988) confirm ing the earlier conclusions on polyphase deformation. This in New research, aided in particu1ar by seismic reflection data and volved emplacement of diabases and gabbrodiabases at 1100 deep drillholes reaching pre-Palaeozoic rocks beneath the 272 Pechora Basin, have confirmed the northeastward extension of BELYAKOVA & STEPANENKO 1991) in what is believed, by the Riphean-?Vendian sedirnentary succession of the Timans BOGATSKY et al. (1996), to have represented an initial collision beneath the several kilometres thickness of Palaeozoic and between the Siberian plate and the extreme northeastern edge younger cover rocks of this basin. The rocks there, however, are of Ba1tica. Terrigenous red bed and tuffaceous deposits of more strongly deformed and metarnorphosed, and comprise not (?)Late Vendian to Cambrian age in the Khoreyver terrane are only sediments but also volcanic rocks (including tholeiitic considered by these same authors to represent molasse deposi basalts and volcanites of island are affinity) and intrusions. tion following the Timanian orogeny. Elsewhere, beneath and There are also fragments of an older basement present. marginal to the Pechora Basin, Lower Ordovician and possibly BELYAKOVA & STEPANENKO (1991) demonstrated the devel Cambrian rocks are lying with marked unconformity above the opment of intense magmatic activity related to the NW-SE zo Timanian deformed complexes. nation and concentrated along the Pechora-Kozhva Fault (their main deep-seated rift zone). Based on geophysical and now pro fuse deep drillhole data, BELYAKOVA & STEPANENKO (1991) and ACKNOWLEDGEMENTS GETSEN (1991) suggested that the pre-Riphean crystalline base ment was broken into a mozaic of microplates separated by We are gratefu1 to Doc. Malgorzata Moczydlowska-Vidal for small Riphean basins. Teetonic inversion, closing of the basins, her examination of the list of microfossils from the Timans and collision of the blocks and magmatic activity have together pro for her opinion on the stratigraphie value of this assemblage. We duced the pre-Pa1aeozoic basement of the Pechora Basin, a re thank also Dr. Valentin Andreichev for making avai1able for us sult of Timanian orogeny involving the accretion and telescop his then unpublished Rb-Sr isotopic ages of rocks in the north ing of new and old lithosphere along this part of the margin of ern Timan. The comments of the referees, Drs. A. Larionov and Baltica. Thus, an originally passive margin was transformed to 1. Golonka, contributed to improvements to an early version of an active one by Late Vendian time. this paper. This account is a contribution to the ongoing work in the Europrobe Timpebar Project, and at the same time a We show aspects of the new model in Fig. 4 as proposed more progress report on the collaboration between the Geological recently by the first author (OLOVYANISHNIKOV et al. 1995). The Survey of Norway and the Komi Research Centre, RAS, main map (Fig. 1) and schematic cross-section (Fig. 4) show the Syktyvkar, Russia. Kolguev and larger Khoreyver massifs, interpreted as older Precambrian terranes, and the so-called Izhma 'rnicroplate', which is the thinned and faulted northeasternmost part of the References Russian Platforrn, rather than a truly separate micropIate. In this scenario the entire Timan ridge between the Western and East Akimova. 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(1995): The struc plisserncnts Baikaliens.- In: Les relations entre Precambrian et Cambrian. ture of the eonjugation zone of the Russian and Pechora plates from gco CNRS ColI. Institute Paris 1957: 91-101. logieal and geophysieal data.- Trans. (Doklady) Russian Aeael. Sei., Earth Schatsky, NS. (1964): On flexures 01' the Donetz-type.- Izbr. Truely JI,"Nauka" Sei. Seetion 351 (8), 1228-1232. 544-552 (in Russian). Olovyanishnikov, VG., Siedlecka, A. & Roberts, D. (1997): Aspeets 01' the gc Siedlecka, A. (1975): Late Preeambrian stratigraphy and strueture 01' the north ology of the Timans, Russia, anel linkages with Varanger Peninsula, NE eastern margin 01' the Fennoseanelian Shielel (East Finnmark-Tirnan Re Norway (exteneleel abstraet).- Nor. Geo!. Unders. BuH. 433: 28-29. gion).- Nor. Geo!. Unelers. 316: 313-348. Raaben. M.B. (1975): Upper Riphean as a unit 01' the general geologieal seale. Sicdlccka, A., Lvubtsov, VV & Negrutsa, vz. (1995): Correlation between Up Inst. Geo!. 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(1980): Geologisk kart over Norge, Berggrunnskart Vadso M 1-15. I: 250000.- Nor. GeoI. Undcrs. Rarnitsyn, WA. (1962): Riphean eleposits 01' the Timans.- Trudy NlJGA 130 (19), Torsvik, TH., Robens. D. & Siedlecka, A. (1995): Palaeomagnetie data from (in Russian). sedimcntary rocks anel elolerite elykes, Kildin Island, Rybaehi, Sreelni and Rarnitsvn, WA. (1968): Strueture 01' the Cenrral Timans.- "Nauka" Leningrael. Varanger Peninsulas, MW Russia anel NE Norway: a rcview.- Nor. Geo!. 22Ö p. (in Russian). ~ . Undcrs. Spee. Pub!. 7: 315.326. Rice, A.H.N (1994): Stratigraphie overlap 01' the Late Proterozoie Vadse and Tschernyschev, T. (1901): On geologieal strueture of the Timans anel on relation Barents Sea Groups and eorrelation aeross the Trollfjorden-Komagclva 01' the Timan Fault to other regions of northern Europe.- Zapiski Fault, Finnmark, North Norway.- Nor. Geo!. Tielsskr 74: 43-57. Mineralogieheskogo Obstcherva 34: 29-33 (in Russian). Rice, A.H.N & Roberts, D. (1995): Very lew-grade metarnorphism 01' Upper Zhuravlev, Vs. (1972): Comparative tectonics ofthe Pechora, Caspian anel North Proterozoie seelimentary rocks of the Rybaehi anel Sreelni Peninsula and Sea exogonal depressions of the European Platform.- 232 Moscow Kilelin Islanel, NW Kola region, Russia.- Nor. GeoI. Unelers. Spee. PubI. 7: "Nauka", 399 pp. (in Russian). 259-270. Zhuravlev, V S. & Gafarov, R.A. (1959): Seheme of tectonic of the north-east Roberts, D. (1995): Prineipal featurcs 01' the struetural geology 01' Rybaehi anel Russian Platform.- Doklaely AN SSSR, Geologia 128, no. 5: 1023-1025 (in Sreelni Peninsulas, Northwest Russin, anel some comparisons with Varanger Russian). Peninsula, North Norway.- Nor. Geo!. Unelers. Spee. Pub!. 7: 247-258. Zhuravlev; VS. & Osadchuk, M.I. (1960): Structural anel facies zonation of the Roberts, D. (1996): Caleelonian and Baikalian teetonic struetures on Varanger Riphean foleleel basemcnt of the Timans.- MOIP BuH., GeoI. Series 35,3: Peninsula, Finnmark, Norway, anel coastal areas 01' Kola Peninsula, NW 89-102 (in Russian with English Summary). Russia.- Nor. Geo!. Unelers. BuH. 431: 59-65. Zliuravl.ev, \~S. & Osadchuk, M.I. (1962): Tectonic position 01' thc Roberts. D. & Nordgulen, 0. (eels.) (1995): Geology of the eastern Finnmark Kisloruchcskaya Formation in composition 01' the Riphean folded basement western Kola Peninsula region.- Nor. GeoI. Undcrs. Spee. PubI. 7, 378 pp. 01' thc Timans.- Doklaely AN SSSR 146,5: 1156-1159 (in Russian). Roberts, D. & Onstott, T'C. (1995): 4°Ar_39Ar laser miereprobe analyses anel Zhuravlev, \,1S., Zabrodin, \,1B., Raaben. M.E. & Chemvy, VG. (1966): On gcochemistry of elolerite dykes frorn the Rybaehi and Sreelni Peninsulas, stratigraphy 01' Basement ofthe Timans.- MOIP BuH., Geo!.Serics 41 ,2: 49 NW Kola, Russia.- Nor. Geo!. Unelers. Spee. PubI. 7: 307-314. 75 (in Russian). 274